Monday, June 09, 2014

In the ongoing battle between alternating and direct current, there may be a new player. Timothy J. Sommerer presented research at APS DAMOP 2014 on a more efficient way to marry alternating and direct currents. Using self-healing materials, Sommerer's new cathode would allow for greater and more effective conversion.

In alternating current, the direction the current travels along the line reverses (or alternates). In the US, the current coming out of your wall reverses 60 times per second. Direct current is a high powered, constant, and direct flow of current. The American power grid runs off of alternating current, but how that came to be was a contentious battle.

The early days of power distribution used direct current (DC), developed by Thomas Edison. But direct current wasn't easily transmitted over long distances, and there was no way to regulate the voltage. As houses began using more appliances that pulled different voltages, regulated voltage became necessary. Nikola Tesla and George Westinghouse (who bought many of Tesla's patents) stepped in with the theory of alternating current (AC), and the 'War of the Currents' began.

Because alternating current could be easily regulated by transformers, and it can travel over long distances, AC was much more cost effective on large scales. Edison grew desperate to keep alternating current from becoming more popular, and waged a campaign to prove that it was dangerous. In addition to electrocuting animals to prove his point, the campaign also led to the invention of the electric chair. Edison couldn't overcome the economic advantages of alternating current (or the fact that it wasn't more dangerous than direct current), and the American electrical grid now runs on AC.

Why is Converting from AC to DC an Issue?

Alternating current worked just fine to power appliances for a long time. But technology has changed since the early 1900s, and the semiconductors in modern electronics need direct current. Semiconductors are in tons of electronics: toys, smoke detectors, cell phones, computers. These things either need batteries, or require that the AC voltage coming out of your wall changes to direct current. If you have a laptop, you're familiar with a box in the middle of the power cord. That box contains all the necessary pieces to convert alternating current into direct current.

This general AC adapter converts the power coming out of the wall into direct current. Image Credit: Wikipedia

Currently, when converting from alternating to direct current, certain components can only handle so much voltage. After a certain point, the components become damaged, and the pieces break down. Sommerer suggests a specific type of cathode that would handle high voltage conversions on large scales. The switch Sommerer and General Electric are developing allows for current to travel through a cathode made of 'self-healing' liquid metal. This would mean that instead of the cathode being damaged in the conversion process when it's slammed with high voltages, it would heal itself.

Practical Applications

Converting alternating and direct currents on such a large scale has exciting applications. Many alternative energy sources, like solar and wind power, produce direct current. With a more efficient and cheaper way to convert the direct current produced into the alternating current electric grid, alternative energy sources become even more effective. Electric cars also use direct current to charge, and a more efficient way to pull direct current from the electric grid could make them cheaper to charge.